Q: Does niyah for fasting have to done loud or verbally or in the heart is ok? I did it in the heart only and i read that this is not valid and have to redo.

A: The Heart as the Seat of Niyyah
The Niyah for fasting does not need to be verbal; the firm resolve within the heart is sufficient. Confusion often arises because some traditions encourage verbalizing to “anchor” the mind, but the core of this worship is internal.
The Hanafi Proof
Imam Abu Hanifa maintained that if the intention exists in the heart, it is fully valid. Amongst the arguments made by the Ahnaf is the is very act of waking for Suhoor, which is also a physical proof of intention. Afterall, you would not be eating at pre-dawn unless you intended to fast.

Allah Certainly Knows Best.

P.s. This idea that things done in the heart as been sufficient does not apply to everything.!